The stereotypical view of African drylands is often of a
parade of elephants marching steadily across endless expanse of savannah
grassland –free to roam. Another staple image, especially of African savannah
documentaries, is the massive wildebeest migration where thousands of
individual animals moving as an aggregation navigating the hazards of the
landscape.
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| Majestic African animal migrations. Main image: "Wildebeest-during-Great-Migration" by Bjørn Christian Tørrissen - Own work by uploader, http://bjornfree.com/galleries.html. Licensed under CC BY-SA 3.0 via Wikimedia Commons. Inset: By Amoghavarsha amoghavarsha.com (Own work) CC BY-SA 3.0 via Wikimedia Commons |
In both of these examples, animals are moving with purpose
for food and water, because this is how an animal survives in a place where
rainfall and vegetation are seasonably variable. These migrations are vital to
the survival of many dryland species. But even at smaller scales, and much less
dramatically than a massive migration, animals need to move through a landscape
to access food, water and mates.
Yet, as human populations spread their influence
by altering ecosystems, they increasingly come in contact with wildlife, and
often compete with them for space, water and agricultural crops. To reduce
these human-wildlife conflicts, people often erect fences to exclude species
and steer them elsewhere. Farmers and ranchers, concerned with their
livelihood, need to exclude grazers from crops and predators from domesticated
animal herds.
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Example of a dryland fence barrier. From: Photo by William I. Boarman, USGS, From press
release: USGS Report Finds Too Few Studies Assess the Success
of Desert Tortoise Recovery Actions, Aug. 10, 2006. http://online.wr.usgs.gov/ocw/g_agassizii/barrier_fence.jpg
While fencing might offer some protection to human
interests, fences can also have broad long-term consequences for animal
populations. However, it is also increasingly appreciated that fencing can be
used as a conservation measure to protect animals from these conflicts and from
illegal hunting. In a thoughtful paper on dryland fencing policy, Durant and
colleagues argue that current fencing policies are often based on limited
information, with an under appreciation of the large-scale, long-term
consequences of fencing nature.
Durant and colleagues argue that fencing can result in
multiple costs and benefits. They cite an important example –fencing to protect
lions. Fences constructed as a lion conservation tool may result in higher lion
population sizes –which seems to valid fencing as a conservation tool; but yet
analyses showed that when carrying capacities are accounted for, fences may not
provide better protection, and further may not be worth the economic and
ecological costs.
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The authors recommend that fencing policy needs to driven by
evidence, and not a reaction to human-wildlife conflict alone. The critical
factors that they suggest are: 1) Economic sustainability of erecting and
maintaining fences, and that the benefits justify the costs; 2) The
permeability of the barrier, because not all species will equally perceive the
fence as a hard edge, and so a fence may not be a well justified as a universal
management tool; 3) Using fencing within a landscape context –fences may
complicate how animals deal with natural features, such as cutting off a
natural river crossing; 4) Connectivity is critical for both the maintenance of
genetic variability within populations and allowing animals to access variable
and ephemeral resources; 5) Ensuring that fences do not interfere with or
reduce the delivery of ecosystem services; and finally 6) Safeguarding the
wellbeing of human communities, especially marginalized and vulnerable groups
that might depend on resources from natural areas.
By creating international policy and regulations based on
these six criteria, Durant and colleagues argue that sensible fencing policy
can be developed, which ensures that fences are used to maximally benefit
humans, animals and natural processes.
